1. Field of the Invention
This invention relates to improvements in a fuel injection system for an internal combustion engine, and more particularly to a locational relationship between fuel discharge openings and air discharge openings formed in a fuel injector fo tthe purpose of improving fuel combustion in the engine.
2. Description of the Prior Art
In case air-fuel mixture is prepared by mixing air and fuel injected from a fuel injector disposed in an intake port of an engine, it is well known that fuel combustion in a combustion chamber of the engine largely depends on an atomization condition of the injected fuel. In view of this, many propositions of simultaneous injection of fuel and air (assist air) from a fuel injector have been made to improve atomization of fuel to be supplied to the combustion chamber under the effect of collision fo the assist air with the injected fuel.
By the way, it is known to provide two intake values for a combustion chamber to improve charging efficiency for purpose of raising engine speed and output power of the engine. In this case, it is necessary to uniformly distribute fuel so from the fuel injector toward the two intake valves. In this regard, it has been proposed that a fuel injector so injects fuel as to form fuel sprays separated and directed into two different directions, as disclosed in Japanese Utility Model Provisional Publication No. 1-61461. The fuel sprays are respectively ejected from two fuel discharge openings of the fuel injector, in which assist air is mixed with fuel in a mixing chamber prior to ejection of fuel from the fuel injector.
However, difficulties have been encountered in the above conventional technique in which fuel is mixed with assist air prior to ejection from the fuel injector, a major amount of fuel adheres on the wall surfaces of the fuel discharge opening and tends to form fuel flow thereon. Thus, in the conventional technique, although the fuel distribution in different directions are accomplished, fuel atomization cannot be effectively achieved.
From a point of view of improving fuel atomization, it may be effective to eject assist air around fuel spray immediately after the fuel spray is ejected from a fuel discharge opening fo the fuel injector, as disclosed in Japanese Utility Model Provisional Publication No. 1-66471. It will be understood that in this conventional technique, fuel vcannot adhere on the wall surface of the fuel ejection opening to form fuel flow. However, in this case, the assist air is rotatingly ejected around fuel spray, and therefore it is difficult to separate the fuel spray into different directions thereby making it impossible to distribute fuel spray toward two separate intake valves.